1. Field of the Invention
This invention relates to improvements in a timer switch.
2. Prior Art
One known timer switch 200 shown in FIG. 1 comprises a synchronous motor 201 in which a rotor, in the form of a permanent magnet having a multi-pole periphery, is rotated in synchronism with a rotating magnetic field caused by a toroidal coil or the like. An interval shaft 202 is journaled in a casing 203, and a bushing 204 is secured to a splined portion 202a of the shaft 202 for rotation therewith. A cam 205 of a disc shape is mounted on a reduced diameter portion or end portion 202b of the shaft 202. The bushing 204 has an integral key portion 204a through which it is keyed to the cam 205. A drive gear 206 is rotatably mounted on a central boss 204b of the bushing 204. The rotation of the motor 201 is transmitted to the drive gear 206 through a reduction gear train 208 comprising a plurality of gears 208.sub.1 to 208.sub.n, so that the cam 205 is rotated in sliding contact with one of electrical contact plates 209 of resilient material for switching electrical current after a preset time interval, as is well known in the art.
A slip friction clutch 207 is provided for rotating or angularly moving the cam 205 independently of the drive gear 206 when the interval shaft 202 is operated manually or otherwise mechanically for setting the timer switch 200. The slip friction clutch 207 comprises a leaf spring in the form of a disc having radially downwardly extending legs 207a. The shaft 202 extends through the leaf spring 207 at its center and is rotatable relative thereto. The leaf spring 207 acts between the stepped portion 202c of the shaft 202 and the drive gear 206 to urge the drive gear 206 into frictional engagement with the bushing 204. With this configuration of the leaf spring 207, however, its dimension in the axial direction of the interval shaft 202 is increased because of the provision of the radially downwardly extending legs 207a. As a result, the timer switch 200 could not be constructed in a compact manner. In addition, the leaf spring 207 could not be manufactured at low costs on account of such a complicated shape.